feat: introduced a token-based theming system across the UI

* feat: added themes system

* feat: smart sidebar auto-hide for files/diff tabs + lower files sidebar threshold

* feat: added Checkbox component and update theming

- Add reusable Checkbox component for toggles across UI
- Replace several inputs with Checkbox in settings and commands panels
- Add DiffIcon and apply surface/border theming to key UI areas

* feat: Add convert-vscode-theme.cjs to convert VS Code themes to OpenChamber format

* refactor: remove unused permission logic from ChatInput

- Remove unused permission rules parsing logic from ChatInput
- Memoize renderTheme in DiffWorkerProvider to avoid unnecessary recalculations
- Remove forceOpaque helper in vscode theme adapter

* fix: guard VSCode theme loading in MarkdownRenderer

* feat: add custom user themes loading and reload

- Load user themes from ~/.config/openchamber/themes at runtime
- Expose /api/config/themes to fetch custom themes
- Allow theme reloading from Settings → Theme → Reload themes in the UI

packages/ui/src/components/multirun/MultiRunLauncher.tsx

@@ -334,7 +334,7 @@ export const MultiRunLauncher: React.FC<MultiRunLauncherProps> = ({
                   type="button"
                   onClick={onCancel}
                   aria-label="Close (Esc)"
-                  className="inline-flex h-9 w-9 items-center justify-center p-2 text-muted-foreground hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary app-region-no-drag"
+                  className="inline-flex h-9 w-9 items-center justify-center p-2 rounded-lg text-muted-foreground hover:text-foreground hover:bg-interactive-hover/50 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary app-region-no-drag"
                 >
                   <RiCloseLine className="h-5 w-5" />
                 </button>
@@ -399,7 +399,7 @@ export const MultiRunLauncher: React.FC<MultiRunLauncherProps> = ({
 
               {/* Setup commands collapsible */}
               <Collapsible open={isSetupCommandsOpen} onOpenChange={setIsSetupCommandsOpen}>
-                <CollapsibleTrigger className="w-full flex items-center justify-between py-1 hover:opacity-80 transition-opacity">
+                <CollapsibleTrigger className="w-full flex items-center justify-between py-1 hover:bg-[var(--interactive-hover)] rounded-md px-1 -mx-1 transition-colors">
                   <p className="typography-ui-label font-medium text-foreground">
                     Setup commands
                     {setupCommands.filter(cmd => cmd.trim()).length > 0 && (